1. Field of the Invention
The invention relates to a device and a method for the classification of transparent components of a material flow. The device comprises an optical detector unit, the allocatable optical axis of which is directed toward the material flow, and at least two units for illuminating the material flow. The at least two illumination units and the detector unit are located on the same side relative to the material flow, that is, in the same half-space spanning over the material flow. The information which the detector unit receives from the components of the material flow is analyzed in a unit which has a classifier. Based on the result of the classification, control signals are generated for a unit for sorting, for example, via actuators, such as blowout nozzles or sorting shunts, or marking or logging. The material flow can be provided in the form of bulk individual objects, for example, in the form of bulk goods, or as a continuously produced coherent material, for example, flat glass or extruded partially-transparent material.
2. Description of the Prior Art
In facilities known for the automatic optical sorting of bulk goods, the material to be sorted, as much as possible in a single-ply layer, is applied on a conveyor belt, conducted through a fall shaft, or shaken over a slide. If a conveyor belt is used, it runs at a velocity of 3 m/s, for example. At the end of the conveyor belt, the material is thrown off of the conveyor belt and flies further in a trajectory. Shortly after the drop edge, an image processing system inspects the material flow. The images recorded by the camera are analyzed by a computer. The components of the bulk good flow, which is to be sorted out, are recognized on the basis of their color and optionally also their shape and blow out of the free flying material flow correctly with the aid of short blasts of compressed air.
In other forms of implementation of optical sorters, the free-flying material flow is not generated via a conveyor belt, but rather the bulk good flow slips over a slide or the bulk good flow is poured properly in the form of a freefalling material flow. For example, reference is made for this purpose to EP 0 146 299 B1, in which a channel sorter is described, in which, for example, a bulk goods flow comprising coffee beans falls through a measuring cell, in which, on one side, an illuminated background is provided and, on the other side, a detector is provided constructed by discrete photo sensors. The bulk goods flow falls in this case vertically through the observation zone, which is formed by the detector, which has a viewing direction toward the background. A high-pressure nozzle unit downstream from the measuring cell in the falling direction of the bulk goods flow selects flawed parts from the bulk good flow. The fundamental mechanism for detecting flawed parts of this type of sorter is based on the measuring acquisition of the difference in color of the flawed parts in contrast to the components of the remaining bulk goods flow.
An important detail in the design of optical sorting units for transparent objects of this type is, above all, the detection of the optical transparency. In particular with bulk goods, this detection is made difficult by the typically randomized location of the transparent objects in the material flow and the often irregular object geometry.
Even with pure materials, the transmission of the material alone is only an index for the type of material if both object shape and also thickness and attitude are known.
For example, upon the inspection of bulk goods, for example, transparent plastic granules—in transmitted light, strong variations of the transmitted radiation occur already due to the at least relatively undefined attitude and the geometry of the objects. Even upon the inspection of transparent spheres in transmitted light, only a round inspection area is obtained, whose boundaries are a function of the system dimensioning and sphere size. Anomalies may only be detected using a transmitted light configuration in this area. Scratches, foreign particles, and cloudiness of the object surface only result in additional attenuation of the transmitted radiation therein, however. Therefore, corresponding classification is not possible or is hardly possible on the basis of the transmission of bulk goods ascertained in a transmitted light configuration.
U.S. Published Application 2006/0016735 A1 describes a sorter for transparent granules, which fall from a belt conveyor along a trajectory through two detector units situated along the trajectory, of which one records the front side of the granules and the other records the rear side of the granules, each using one camera and one background associated with the camera. By comparing front and rear recordings, the transparency of the components can be concluded and flawed parts can be separated out using a compressed air nozzle on the basis of a criterion. The camera images exclusively acquire light components reflected on the granule surfaces in this configuration, so that an acquisition of flaws enclosed in the granules is not possible.
U.S. Pat. No. 5,442,446 describes a device for examining transparent containers, in particular in regard to their fill level, which provides a light source, whose light passes coaxially in the viewing direction of a detector through a container to be examined, is reflected on a retroreflector situated to the rear of the container, and is acquired by the detector. In addition, two further light sources are provided to the rear of the container, whose emitted light beams penetrate the container in transmission and are also acquired by the detector.
EP 0 379 281 describes a device for examining fabric structures, light from a light source being directed for this purpose via a corresponding deflection mirror onto the surface of a fabric substrate to be examined, under which a retroreflector is provided. The light beams reflected back on themselves are also acquired by a detector unit in this case.
EP 0 372 241 B1 describes an optic configuration for three-dimensional shape acquisition, using which irregularities of a transparent film may be acquired in particular. Light from a light source passes through the film in transmission and is reflected on a retroreflector attached in the beam direction behind the film. The reflected light component is acquired by a video camera for further analysis.